The present invention relates to a thrust foil air bearing, and more particularly to a thrust foil air bearing which can enhance the load capacity. The present invention provides a ramp of top foils to generate uniformly distributed and higher pressure inside the bearing without excessive pressure change or drop in the rotational direction of a bearing disc so that the total pressure in the bearing increases and the load capacity is improved.
A foil air bearing is a bearing which supports loads by air pressure generated by the incoming air having viscosity between a rotor or a bearing disc and a foil structure contacting therewith at high speed rotation of the rotor.
With reference to FIGS. 1 and 2, a thrust foil air bearing 100 is provided with a thrust plate 60, and a bump foil 80 is arranged thereon and a top foil 90 is disposed along the top of the bump foil 60. An edge 94 of the top foil 90 is attached to the thrust plate 60 and the top foil 90 is extended along the top of a bump 8 of the bump foil 80 through a ramp 99.
When a bearing disc 20 rotates together with a rotor 10, air having viscosity flows in along the ramp 99 of the top foil 90 and pressure is formed between the top foil 90 and the disc 20. The pressure formed there between supports the loads.
With reference to FIG. 3, in general, the ramp 99 of the top foil is straight or assigned an arbitrary shape adaptable for easy production. In this case, the pressure increases sharply at A where the ramp terminates, however, the pressure falls down in the area B due to the side leakage effect caused by increased pressure at A. As a result, total pressure decreases and the load capacity reduces.
The load capacity is determined by the total air pressure formed in the bearing and it is necessary to raise the integrated total air pressure not the peak value. The present invention provides a novel and unique ramp structure which can raise the total air pressure and increase the load capacity.